Heretofore, conveyor chain-driven trolleys have been made of steel and metallic components requiring considerable and expensive lubrication installations and maintenance. Such trolleys are of very substantial weight, adding materially to the load on the conveyor and consequent high energy consumption, having a relatively short service life before replacement or service maintenance is required, readily subject to corrosion and early failure in certain chemically active environments, and having other limitations which the instant invention avoids.
Among the advantages achieved by the conveyor trolley structure of this invention are
a. The coefficient of friction of the plastic material used in the trolley stub axle, bearings and wheel components is extremely low and thus lubrication of the moving parts is not required. This feature also eliminates expensive lubrication equipment, facilities, installations and maintenance. In addition, in some applications, as for instance in food processing plants, the elimination of lubricants removes the possibility of such contaminants dripping upon fresh or processed foods carried by or located under the conveyor system.
b. There is a weight reduction of about 80% or more for the new plastic trolleys, in comparison to the currently used steel trolleys. This weight reduction not only extends the wear life of the monorail itself and the service life of the entire conveyor system, it will also lower the size requirements for the drive motors and mechanism with consequent reduction in energy consumption. The current service life of steel trolley conveyor systems is estimated to be from about 5 to 7 years. The inventive plastic trolley construction should at least double the service life of the monorail system.
c. The plastic trolley construction of this invention is extremely advantageous in areas where severely corrosive chemical vapors are present, such for example where caustic wash solutions are sprayed, causing a breakdown in lubrication which in turn destroys the roller bearings in the present steel trolley assemblies. The same results occur in the presence of phosphate solutions. Millions of dollars are being spent to automatically lubricate overhead monorail conveyor systems and to seal off the trolley assemblies while they pass through these severely corrosive areas.
d. By virtue of its design, the inventive trolley construction permits lower replacement cost for any component. This is not true for the presently used steel assemblies. For example, if a steel ball bearing trolley wheel should fail, not only the wheel but the entire side arm must be replaced. In the instant invention, the individual unitary components are simply and readily replaceable, at a very substantially lower cost.
e. Because of the low coefficient of friction for the plastic pendant member secured to the trolley arms, the holes in these pendants, from which the trolley hanger rods are secured by metal screws, will not become elongated due to wear. If the pendant becomes overstressed, it will simply break at the hole.
f. The plastic trolley construction effects a tremendous reduction in decible readings for the conveyor zone, a great advantage in terms of noise abatement and/or pollution. Overhead steel trolley monorail installations, particularly if they are old, become extremely noisy due to mismatches and unevenness in weld joints along the I-beam monorail.
g. In certain installations of the plastic conveyor trolley having a stub axle and wheel according to the disclosure in U.S. Pat. No. 4,228,738, it was found that the energy load required to initiate movement of the conveyor system was somewhat higher than that required to initiate conveyor translation of the conventional steel trolley system, although once the conveyor system was in motion the energy load to maintain movement of the plastic trolleys was lower than that for the steel trolley system.
The plastic trolley construction of this invention has some additional advantages.
(1) The plastic conveyor trolley with roller bearings reduces the initial drag of the plastic stub axle and wheel combination on start-up of the conveyor system. Only line, not surface contact, is made by the plastic roller bearings on the plastic stub axle and plastic wheel, thereby significantly reducing the initial pull load of the conveyor system.
(2) The super tough nylon plastic resin allows for engineering a precision assembly. No secondary drilling of holes or alignment of details need be performed prior to attaching the trolleys to the monorail.
(3) Color coding of the plastic trolley assemblies will enable part identification to be more readily made on mixed model conveyor installations. Also, the assemblies can be colored brightly to signal a moving object, even though color coding may not be required under OSHA specifications.
(4) By designing the trolley components of the moldable Zytel.RTM.ST 801 plastic nylon material, the trolley arms, stub axle, roller bearings, wheels and pendant member are each engineered to be readily replaceable in minutes, resulting in minimum downtime of the conveyor system.
The Zytel.RTM.ST 801 plastic nylon material, used in the fabrication of applicant's trolley components, is a super tough nylon resin material produced by E. I. DuPont de Nemours & Co. (Inc.) of Wilmington, Del. 19898. Another material which can be used for the roller bearings is DuPont's Delrin.RTM. crystalline plastic, an acetal resin material made by the polymerization of formaldehyde. The Zytel.RTM. plastic resin can be mixed with a fiber glass concentrate to add further strength to the nylon material. The amount of such fiber glass additive is proportional to the weight load of the conveyor trolley assembly. As the load or weight requirements of the trolley assembly increase, the percentage of fiber glass used with the nylon resin is also increased.